OTREC-RR-10-12

This study addressed two types of freeway traffic transitions: transitions near a merge, and transitions along shock waves during the onset and dissipation of queues at four freeway sites. Individual vehicle trajectory data were analyzed for studying transitions near a merge. The length of a transition zone was measured by analyzing the spatial changes in flow, density and speed along kinematic waves near a merge. The length of transition in terms of flow, density and speed was respectively around 90m, 120m and 180m indicating that the transition in flow occurs over a short distance while the transition in speed occurs in much longer space. The dynamics of the transition zone were explored by analyzing the relationship among the transition durations, rates and various traffic and geometric variables. Transition rates tend to be larger upstream of an on-ramp while they tend to be smaller upstream of an off-ramp, indicating that inflows and outflows have different effects on transition characteristics.